Quantization and inverse quantization for audio

Abstract

An audio encoder and decoder use architectures and techniques that improve the efficiency of quantization (e.g., weighting) and inverse quantization (e.g., inverse weighting) in audio coding and decoding. The described strategies include various techniques and tools, which can be used in combination or independently. For example, an audio encoder quantizes audio data in multiple channels, applying multiple channel-specific quantizer step modifiers, which give the encoder more control over balancing reconstruction quality between channels. The encoder also applies multiple quantization matrices and varies the resolution of the quantization matrices, which allows the encoder to use more resolution if overall quality is good and use less resolution if overall quality is poor. Finally, the encoder compresses one or more quantization matrices using temporal prediction to reduce the bitrate associated with the quantization matrices. An audio decoder performs corresponding inverse processing and decoding.

1. In a computing device that implements an audio decoder, a computer-implemented method comprising:
 receiving, at the computing device that implements the audio decoder, encoded audio information, the encoded audio information including information for plural quantization matrices; 
 decompressing, at the computing device that implements the audio decoder, at least one of the plural quantization matrices using temporal prediction; and 
 with the computing device that implements the audio decoder, decoding the encoded audio information, including applying the plural quantization matrices in inverse quantization, wherein the resolution of the plural quantization matrices varies during the decoding. 
 
     
     
       2. The method of  claim 1  wherein the resolution varies due to changing of quantization of information for the plural quantization matrices. 
     
     
       3. The method of  claim 1  wherein the resolution varies due to changing of quantization of elements of the plural quantization matrices. 
     
     
       4. The method of  claim 1  wherein the resolution is set on a channel-by-channel basis. 
     
     
       5. The method of  claim 1  wherein the encoded audio information is in more than two channels. 
     
     
       6. The method of  claim 1  wherein the temporal prediction is from an anchor matrix to the at least one of the plural quantization matrices within a channel. 
     
     
       7. In a computing device that implements an audio decoder, a computer-implemented method comprising:
 receiving, at the computing device that implements the audio decoder, encoded audio information for audio, the encoded audio information including information for plural weight factors, wherein each of the plural weight factors indicates a weight value for one or more frequency bands for a time window of the audio; and 
 with the computing device that implements the audio decoder, decoding the audio using the encoded audio information, including:
 selecting a weight factor resolution from plural available weight factor resolutions; and 
 reconstructing the plural weight factors using the selected weight factor resolution and, for at least one of the plural weight factors, temporal prediction. 
 
 
     
     
       8. The method of  claim 7  wherein:
 the encoded audio information includes information indicating the selected weight factor resolution, wherein bitstream syntax permits the selected weight factor resolution to change over time during the decoding of the audio; 
 the encoded audio information further includes entropy coded differences for at least some of the plural weight factors; and 
 the reconstructing the plural weight factors includes inverse quantizing the plural weight factors according to the selected weight factor resolution. 
 
     
     
       9. The method of  claim 7  wherein the plural weight factors include a first set of weight factors for a previous time window and a second set of weight factors for a current time window, and wherein the reconstructing using temporal prediction includes, for a current weight factor in the second set of weight factors:
 determining a corresponding weight factor in the first set of weight factors; 
 entropy decoding a difference between the current weight factor and the corresponding weight factor; and 
 combining the corresponding weight factor with the difference between the current weight factor and the corresponding weight factor. 
 
     
     
       10. The method of  claim 9  wherein the first set of weight factors and the second set of weight factors have the same number of weight factors, and wherein the determining the corresponding weight factor comprises determining which weight factor in the first set of weight factors is for the same one or more frequency bands as the current weight factor in the second set of weight factors. 
     
     
       11. The method of  claim 9  wherein the first set of weight factors and the second set of weight factors have different numbers of weight factors, and wherein the determining the corresponding weight factor comprises:
 determining one or more current frequency bands for the current weight factor; 
 mapping the one or more current frequency bands to a corresponding frequency band for the first set of weight factors; and 
 assigning the corresponding weight factor as the weight factor in the first set of weight factors that is for the corresponding frequency band. 
 
     
     
       12. The method of  claim 9  wherein the first set of weight factors is decoded without using temporal prediction, wherein the second set of weight factors is decoded using temporal prediction relative to the first set of weight factors, and wherein a third set of weight factors for a later time window after the current time window is also decoded using temporal prediction relative to the first set of weight factors. 
     
     
       13. The method of  claim 7  wherein the plural available weight factor resolutions include one or more of 1 dB, 2 dB, 3 dB and 4 dB. 
     
     
       14. A computing device that implements an audio encoder, the computing device comprising a processor, memory and storage that stores computer-executable instructions for causing the processor to perform a method comprising:
 receiving audio; and 
 encoding the audio to produce encoded audio information, the encoded audio information including information for plural weight factors, wherein each of the plural weight factors indicates a weight value for one or more frequency bands for a time window of the audio, and wherein the encoding the audio includes:
 selecting a weight factor resolution from plural available weight factor resolutions; and 
 encoding the plural weight factors using the selected weight factor resolution and, for at least one of the plural weight factors, temporal prediction. 
 
 
     
     
       15. The computing device of  claim 14  wherein the encoding the audio further includes generating the plural weight factors and quantizing the plural weight factors according to the selected weight factor resolution, and wherein the encoded audio information includes information indicating the selected weight factor resolution, wherein bitstream syntax permits the selected weight factor resolution to change over time during the encoding of the audio. 
     
     
       16. The computing device of  claim 14  wherein the plural weight factors include a first set of weight factors for a previous time window and a second set of weight factors for a current time window, and wherein the encoding using temporal prediction includes, for a current weight factor in the second set of weight factors:
 determining a corresponding weight factor in the first set of weight factors; 
 determining a difference between the current weight factor and the corresponding weight factor; and 
 entropy coding the difference between the current weight factor and the corresponding weight factor. 
 
     
     
       17. The computing device of  claim 16  wherein the first set of weight factors and the second set of weight factors have the same number of weight factors, and wherein the determining the corresponding weight factor comprises determining which weight factor in the first set of weight factors is for the same one or more frequency bands as the current weight factor in the second set of weight factors. 
     
     
       18. The computing device of  claim 16  wherein the first set of weight factors and the second set of weight factors have different numbers of weight factors, and wherein the determining the corresponding weight factor comprises:
 determining one or more current frequency bands for the current weight factor; 
 mapping the one or more current frequency bands to a corresponding frequency band for the first set of weight factors; and 
 assigning the corresponding weight factor as the weight factor in the first set of weight factors that is for the corresponding frequency band. 
 
     
     
       19. The computing device of  claim 16  wherein the first set of weight factors is encoded without using temporal prediction, wherein the second set of weight factors is encoded using temporal prediction relative to the first set of weight factors, and wherein a third set of weight factors for a later time window after the current time window is also encoded using temporal prediction relative to the first set of weight factors. 
     
     
       20. The computing device of  claim 14  wherein the plural available weight factor resolutions include one or more of 1 dB, 2 dB, 3 dB and 4 dB.